Upload
ringo
View
47
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Special Design and Construction Considerations. 2009 PDCA Professor Pile Institute. Patrick Hannigan GRL Engineers, Inc. SPECIAL DESIGN CONSIDERATIONS. Time effects on pile capacity. Pile driveability Scour Densification effects on pile capacity - PowerPoint PPT Presentation
Citation preview
Special Design and Special Design and Construction Construction
ConsiderationsConsiderations
2009 PDCA Professor Pile 2009 PDCA Professor Pile InstituteInstitute
Patrick Hannigan
GRL Engineers, Inc.
• Time effects on pile capacity. Time effects on pile capacity.
• Pile driveabilityPile driveability
• ScourScour
• Densification effects on pile capacityDensification effects on pile capacity
• AAdditional design and construction topics in FHWA Pile Manual Chapters 9.9 and 9.10
SPECIAL DESIGN SPECIAL DESIGN CONSIDERATIONSCONSIDERATIONS
590
560
530
500
470
430
14” CEP
TIME EFFECTS ON PILE TIME EFFECTS ON PILE CAPACITYCAPACITY
Time dependent changes in pile capacity occur with time.
Soil SetupSoil Setup RelaxationRelaxation
Soil setupSoil setup is a time dependent increaseincrease in the static pile capacity.
Large excess positive pore pressures are often generated during pile driving.
Soil setup frequently occurs for piles driven in saturated clayssaturated clays as well as loose to medium loose to medium dense silts and fine sandsdense silts and fine sands as the excess pore pressures dissipate.
The magnitude of soil setup depends on soil characteristics as well as the pile material and type.
SOIL SETUPSOIL SETUP
1 d
ay1
day
10 d
ays
10 d
ays
100
day
s10
0 d
ays
1000
day
s10
00 d
ays
log timelog time
cap
acit
yca
pac
ity
Technically desirable
Technically desirableEconomically desirable
Economically desirable
Restrike testing generally performedRestrike testing generally performed
1 to 10 days after installation1 to 10 days after installation
Soil SetupSoil Setup Soil SetupSoil Setup
When to test?
When to test?
Semilog-linear process
Semilog-linear process
SOIL SETUP FACTORSOIL SETUP FACTOR
The soil setup factor is defined as failure load
determined from a static load test divided by the
ultimate capacity at the end of driving.
TABLE 9-20 SOIL SETUP FACTORS(after Rausche et al., 1996)
Predominant Soil Type Along Pile
Shaft
Range inSoil Set-up
Factor
RecommendedSoil Set-up
Factors*
Number of Sitesand (Percentage
of Data Base)
Clay 1.2 - 5.5 2.0 7 (15%)
Silt - Clay 1.0 - 2.0 1.0 10 (22%)
Silt 1.5 - 5.0 1.5 2 (4%)
Sand - Clay 1.0 - 6.0 1.5 13 (28%)
Sand - Silt 1.2 - 2.0 1.2 8 (18%)
Fine Sand 1.2 - 2.0 1.2 2 (4%)
Sand 0.8 - 2.0 1.0 3 (7%)
Sand - Gravel 1.2 - 2.0 1.0 1 (2%)
* - Confirmation with Local Experience Recommended
RelaxationRelaxation is a time dependent decreasedecrease in the static pile capacity.
During pile driving, dense soils may dilate thereby generating negative pore pressures and temporarily higher soil resistance.
Relaxation has been observed for piles driven in
dense, saturated non-cohesive silts, fine sands, dense, saturated non-cohesive silts, fine sands,
and some shalesand some shales.
RELAXATIONRELAXATION
The relaxation factor is defined as failure load
determined from a static load test divided by the
ultimate capacity at the end of driving.
Relaxation factors of 0.5 to 0.9 have been reported
in case histories of piles in shales.
Relaxation factors of 0.5 and 0.8 have been
observed in dense sands and extremely dense
silts, respectively.
RELAXATION FACTORRELAXATION FACTOR
TIME EFFECTS ON PILE TIME EFFECTS ON PILE DRIVEABILITY AND CAPACITYDRIVEABILITY AND CAPACITY
Time dependent soil strength changes that
affect the soil resistance at the time of driving
should be considered during the design stage.
• Remolded shear strength in claysRemolded shear strength in clays
• Estimate of pore pressures during drivingEstimate of pore pressures during driving
• Soil setup / relaxation factorsSoil setup / relaxation factors
PILE PILE DRIVEABILITYDRIVEABILITY
PILE DRIVEABILITYPILE DRIVEABILITY
Pile driveability refers to the ability of a pile to
be driven to the desired depth and / or capacity
at a reasonable driving resistance without
exceeding the material driving stress limits.
Soil Profile Soil Profile Illustrating Illustrating Driveability Driveability
ConsiderationConsiderationss
Estimated Tip EL 14” Pipe
Estimated Tip EL 12” H-pile
FACTORS AFFECTING FACTORS AFFECTING PILE DRIVEABILITYPILE DRIVEABILITY
• Driving system characteristicsDriving system characteristics
• Pile material strengthPile material strength
• Pile impedance, EA/CPile impedance, EA/C
• Dynamic soil responseDynamic soil response
Primary factor controlling driveability
PILE DRIVEABILITYPILE DRIVEABILITY
Pile driveability should be checked during the
design stagedesign stage for all driven piles.
Pile driveability is particularly critical for closed end
pipe piles.
PILE DRIVEABILITY PILE DRIVEABILITY EVALUATION DURING DESIGN EVALUATION DURING DESIGN
STAGESTAGE1. Wave Equation Analysis1. Wave Equation Analysis
Computer analysis that does not require a pile to be driven.
2. Dynamic Testing and Analysis2. Dynamic Testing and Analysis
Requires a pile to be driven and dynamically tested.
3. Static Load Tests3. Static Load Tests
Requires a pile to be driven and statically load tested.
46 ft
20 ft
Silty Clay
= 127 lbs / ft3
qu = 5.5 ksf
Dense, Silty F-M Sand
= 120 lbs / ft3
= 35˚
3 ft
Soil Profile – 12.75 In Soil Profile – 12.75 In CEPCEP
Student Exercise #2 RevisitedStudent Exercise #2 Revisited
Static analysis indicates a 12.75 in O.D. closed-end pipe pile driven to 63 ft below grade can develop an ultimate capacity of 420 kips. A static load test will be used for construction control. No special design conditions exist (scour, downdrag, etc.). Therefore, a maximum axial design load of _______ kips can be used.
210210
Pick Pile Section – (Appendix C2-Pick Pile Section – (Appendix C2-4)4)
Given: 12.75 in O.D. closed-end pipe pile
Select: wall thickness – try 0.109 in wall (lowest cost)
ASTM A-252 Grade 3 steel – FY = 45 ksi
28 day concrete strength – f’c = 5 ksi
Check Allowable Design Load Check Allowable Design Load (10-5)(10-5)
Design Load = 0.25 (FY)(steel area) + 0.40(f’c)(concrete area)
= 0.25(45 ksi)(4.33 in2) + 0.40(5 ksi)(123.0 in2)
= 48.7 kips + 246.0 kips
= 294 kips
Is this section suitable for an 420 kip ultimate pile capacity? ____YesYes
Check Pile DriveabilityCheck Pile Driveability
Driveability Requirements:
Driving resistance between ____ and ____ blows/ft
(see pg 11-15)
Driving stress limit of 0.9(FY) = _____ ksi
(see pg 10-5)
1201203030
40.540.5
Check Pile DriveabilityCheck Pile Driveability
Determine Hammer Size:
Rated energy for 420 kip ultimate capacity ____ ft-kips
(see pg 21-36)
Select trial hammer __________________________
(see Appendix D-1)
Perform Wave Equation Analysis
3838
Delmag D-16-32 (ID #5)Delmag D-16-32 (ID #5)
GRLWEAPGRLWEAP
DriveabilityDriveability
ResultsResults
For D-16-32For D-16-32
Piles Subject to ScourPiles Subject to Scour
Piles Subject to ScourPiles Subject to Scour
Aggradation / Degradation Scour
Types of ScourTypes of Scour
Local Scour
Contraction and General Scour
- Long-term stream bed elevation changes
- Removal of material from immediate vicinity of foundation
- Erosion across all or most of channel width
Pile Design Pile Design Recommendations in Soils Recommendations in Soils
Subject to ScourSubject to Scour1.1. Reevaluate foundation design relative to Reevaluate foundation design relative to
pile length, number, size and typepile length, number, size and type
2.2. Design piles for additional lateral restraint Design piles for additional lateral restraint and column action due to increase in and column action due to increase in unsupported lengthunsupported length
3.3. Local scour holes may overlap, in which Local scour holes may overlap, in which case scour depth is indeterminate and case scour depth is indeterminate and may be deeper. may be deeper.
Pile Design Pile Design Recommendations in Soils Recommendations in Soils
Subject to ScourSubject to Scour4. Perform design assuming all material above 4. Perform design assuming all material above scour line has been removed.scour line has been removed.
5. Place top of footing or cap below long-term 5. Place top of footing or cap below long-term scour depth to minimize flood flow scour depth to minimize flood flow obstruction.obstruction.
6. Piles supporting stub abutments in 6. Piles supporting stub abutments in embankments should be driven below the embankments should be driven below the thalweg elevation. thalweg elevation.
Densification Effects on Pile Densification Effects on Pile CapacityCapacity
Densification Effects on Densification Effects on Pile CapacityPile Capacity
Densification can result in the pile capacity as Densification can result in the pile capacity as
well as the pile penetration resistance to well as the pile penetration resistance to
driving being significantly greater than that driving being significantly greater than that
calculated for a single pile.calculated for a single pile.
Added confinement from cofferdams or the Added confinement from cofferdams or the
sequence of pile installation can further sequence of pile installation can further
aggravate a densification problem.aggravate a densification problem.
Densification Densification Effects on Pile Effects on Pile
CapacityCapacityPotential densification effects should be Potential densification effects should be
considered in the design stage. Studies considered in the design stage. Studies
indicate an increase in soil friction angle of up indicate an increase in soil friction angle of up
to 4to 4˚ would not be uncommon for piles in loose ˚ would not be uncommon for piles in loose
to medium dense sands. to medium dense sands.
A lesser increase in friction angle would be A lesser increase in friction angle would be
expected in dense sands or cohesionless soils expected in dense sands or cohesionless soils
with a significant fine content.with a significant fine content.
Vibrations from pile driving sometimes perceived as a problem.
Vibrations can cause damage.
Vibrations can cause soil densification and settlement.
Pile driving vibrations often a perceived problem than an actual problem and can often be controlled by construction procedures
PDCA database – www.piledrivers.org
Pile Driving Induced Pile Driving Induced VibrationsVibrations
• 220 piles monitored
• 2 failed vibration criteria
• No significant movement (> 1 mm) recorded by crack monitoring devices
• No damage to masonry facade
1 10 1002 4 6 8 20 40 60 80
Vibration Frequency (Hz)
0.1
1
2
3
Pea
k P
arti
cle
Vel
oci
ty (
in/s
ec)
1 10 1002 4 6 8 20 40 60 80
1 0
2 0
4 0
6 0
8
6
4
2
Peak P
article Velo
city (mm
/sec)
U SBM (1985)
H ajduk et a l. (2004) - N ew
H ajduk et a l. (2004) - O lder/H istoric
H P 12x53 P iles
12 in O D C EP P iles
123
124
Charleston SC ProjectCharleston SC Project• Hydraulic hammer (30 ft-kip)
• HP 12 x53 H-piles
• Predrill 12” diameter hole to 40 ft.
Any QuestionsAny Questions